Organic cation transporters (OCT) 1, 2 and 3 and novel organic cation transporters (OCTN) 1 and 2 of the solute carrier 22 (SLC22) family are involved in the cellular transport of endogenous compounds such as neurotransmitters, l-carnitine and ergothioneine. OCT/Ns have also been implicated in the transport of xenobiotics across various biological barriers, for example biguanides and histamine receptor antagonists. In addition, several drugs used in the treatment of respiratory disorders are cations at physiological pH and potential substrates of OCT/Ns. OCT/Ns may also be associated with the development of chronic lung diseases such as allergic asthma and chronic obstructive pulmonary disease (COPD) and, thus, are possible new drug targets. As part of the Special Issue “Physiology, Biochemistry and Pharmacology of Transporters for Organic Cations”, this review provides an overview of recent findings on the (patho)physiological and pharmacological functions of organic cation transporters in the lung.

Baru nuts (Dipteryx alata Vog.) are a native species from Brazil, rich in phenols and other antioxidants, with high socioeconomic value and possible pharmaceutical applications. Here we investigated baru nut ethanolic extract (BNEE) antioxidant and wound healing activities in human NCI-H441 and A549 lung epithelial cell lines for a possible use in conditions related to oxidative stress and wound healing impairments, such as chronic obstructive pulmonary disease (COPD). BNEE was characterised with high DPPH free radical scavenging activity and high total phenolics content, amongst them gallic acid, that was identified and quantified by HPLC. BNEE was not cytotoxic at concentrations studied, reduced the levels of reactive oxygen species before and during oxidative stress and increased wound healing in cell monolayers. These are the first steps to investigate the beneficial properties of baru in diseases related to oxidative stress and wound healing impairments such as COPD. Graphical Abstract

Multidrug resistance-associated protein 1 (ABCC1) is abundantly expressed at the lung epithelial barrier, where it may influence the pulmonary disposition of inhaled drugs and contribute to variability in therapeutic response. Aim of this study was to assess the impact of ABCC1 on the pulmonary disposition of 6-bromo-7-¹¹C-methylpurine (¹¹C-BMP), a prodrug radiotracer which is intracellularly conjugated with glutathione to form the ABCC1 substrate S-(6-(7-¹¹C-methylpurinyl))glutathione (¹¹C-MPG). Methods: Groups of Abcc1(-/-) rats, wild-type rats pretreated with the ABCC1 inhibitor MK571 and wild-type control rats underwent dynamic PET scans after administration of ¹¹C-BMP intravenously (i.v.) or by intratracheal aerosolization (i.t.). In vitro transport experiments were performed with unlabeled BMP in the human distal lung epithelial cell line NCI-H441. Results: Pulmonary kinetics of radioactivity were significantly different between wild-type and Abcc1(-/-) rats, but differences were more pronounced after i.t. than after i.v. administration. After i.v. administration lung exposure (AUClung) was 77% higher and the elimination slope of radioactivity washout from the lungs (kE,lung) was 70% lower, whereas after i.t. administration AUClung was 352% higher and kE,lung was 86% lower in Abcc1(-/-) rats. Pretreatment with MK571 decreased kE,lung by 20% after i.t. radiotracer administration. Intracellular accumulation of MPG in NCI-H441 cells was significantly higher and extracellular efflux was lower in presence than in absence of MK571. Conclusion: PET with pulmonary administered ¹¹C-BMP can measure ABCC1 activity at the lung epithelial barrier and may be applicable in humans to assess the effects of disease, genetic polymorphisms or concomitant drug intake on pulmonary ABCC1 activity.

Multidrug resistance-associated protein-1 (MRP1/ABCC1) is highly expressed in human lung tissues. Recent studies suggest that it significantly affects the pulmonary disposition of its substrates, both after pulmonary and systemic administration. To better understand the molecular mechanisms involved, we studied the expression, subcellular localization and activity of MRP1 in freshly isolated human alveolar epithelial type 2 (AT2) and type 1-like (AT1-like) cells in primary culture, and in the NCI-H441 cell line. Moreover, the effect of cigarette smoke extract (CSE) and a series of inhaled drugs on MRP1 abundance and activity was investigated in vitro. MRP1 expression levels were measured by q-PCR and immunoblot in AT2 and AT1-like cells from different donors and in several passages of the NCI-H441 cell line. The subcellular localization of the transporter was studied by confocal laser scanning microscopy and cell surface protein biotinylation. MRP1 activity was assessed by bidirectional transport and efflux experiments using the MRP1 substrate, 5(6)-carboxyfluorescein [CF; formed intracellularly from 5(6)-carboxyfluorescein-diacetate (CFDA)] in AT1-like and NCI-H441 cell monolayers. Furthermore, the effect of CSE as well as several bronchodilators and inhaled corticosteroids on MRP1 abundance and CF efflux was investigated. MRP1 protein abundance increased upon differentiation from AT2 to AT1-like phenotype, however, ABCC1 gene levels remained unchanged. MRP1 abundance in NCI-H441 cells were comparable to those found in AT1-like cells. The transporter was detected primarily in basolateral membranes of both cell types which was consistent with net basolateral efflux of CF. Likewise, bidirectional transport studies showed net apical-to-basolateral transport of CF which was sensitive to the MRP1 inhibitor MK-571. Budesonide, beclomethasone dipropionate, salbutamol sulfate, and CSE decreased CF efflux in a concentration-dependent manner. Interestingly, CSE increased MRP1 abundance, whereas budesonide, beclomethasone dipropionate, salbutamol sulfate did not have such effect. CSE and inhaled drugs can reduce MRP1 activity in vitro, which implies the transporter being a potential drug target in the treatment of chronic obstructive pulmonary disease (COPD). Moreover, MRP1 expression level, localization and activity were comparable in human AT1-like and NCI-H441 cells. Therefore, the cell line can be a useful alternative in vitro model to study MRP1 in distal lung epithelium.

Azole-resistant Aspergillus fumigatus (A. fumigatus) is an emerging worldwide pathogen. Pulmonary aspergillosis primarily affects severely immunocompromised patients and is also a particularly critical condition for cystic fibrosis (CF) patients. A recently designed gallium polypyridyl catecholate complex, GaS1, has previously demonstrated in vitro and in vivo antimicrobial activity against Gram-negative bacteria. In the present work GaS1 activity was assessed against A. fumigatus clinical isolates in a novel air-liquid-interface lung infection model, mimicking the conditions found in the CF airways. Furthermore, in this study both a solution for nebulisation and dry powders for inhalation were developed with a view to optimising GaS1 delivery to the lung. The solution for nebulisation was characterised for its osmolality and pH, while the dry powders were characterised by scanning electron microscopy, powder X-ray diffraction, thermal analysis and laser light scattering particle size analysis. The aerodynamic deposition profiles of all formulations were determined using a next generation impactor. GaS1, tested in a concentration range of 0.016-0.5 mg/mL, inhibited the growth of A. fumigatus lung isolates in a complex host-environment-mimicking medium at the non-toxic concentration of 0.063 mg/mL. A marked dose-dependent antifungal activity of GaS1 was also observed in the presence of differentiated human distal lung epithelial cells (NCI-H441) at the air liquid interface, with nearly no fungal growth detected at the macroscopic and microscopic level. A solution for nebulisation and three different dry powder inhaler formulations, prepared by spray-drying GaS1 with different concentrations of L-leucine, displayed suitable aerodynamic characteristics for GaS1 delivery to the lungs, while maintaining excellent antifungal activity. Overall, the results obtained highlight the potential of gallium-polypyridyl catecholate complexes for the management of difficult-to-treat A. fumigatus pulmonary infections.